rust-lang/rust
1
0
Fork 0
Code Issues Pull Requests Actions 1 Packages Projects Releases Wiki Activity

Update ABI compatibility docs about null-pointer-optimized enums.

Browse Source 
Add that the enum must be `#[repr(Rust)]` and not `#[repr(packed)]` or `#[repr(align)]` in order to be ABI-compatible with its null-pointer-optimized field.
This commit is contained in:
zachs18
2025-06-03 00:22:10 -05:00
committed by Zachary S
parent 99426c570e
commit c0851d76c9
1 changed files with 3 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
library/core/src/primitive_docs.rs
View File

@@ -1833,6 +1833,8 @@ mod prim_ref {}
/// - If `T` is guaranteed to be subject to the [null pointer /// - If `T` is guaranteed to be subject to the [null pointer
/// optimization](option/index.html#representation), and `E` is an enum satisfying the following /// optimization](option/index.html#representation), and `E` is an enum satisfying the following
/// requirements, then `T` and `E` are ABI-compatible. Such an enum `E` is called "option-like". /// requirements, then `T` and `E` are ABI-compatible. Such an enum `E` is called "option-like".
/// - The enum `E` uses the [`Rust` representation], and is not modified by the `align` or
/// `packed` representation modifiers.
/// - The enum `E` has exactly two variants. /// - The enum `E` has exactly two variants.
/// - One variant has exactly one field, of type `T`. /// - One variant has exactly one field, of type `T`.
/// - All fields of the other variant are zero-sized with 1-byte alignment. /// - All fields of the other variant are zero-sized with 1-byte alignment.
@@ -1906,6 +1908,7 @@ mod prim_ref {}
/// [`Pointer`]: fmt::Pointer /// [`Pointer`]: fmt::Pointer
/// [`UnwindSafe`]: panic::UnwindSafe /// [`UnwindSafe`]: panic::UnwindSafe
/// [`RefUnwindSafe`]: panic::RefUnwindSafe /// [`RefUnwindSafe`]: panic::RefUnwindSafe
/// [`Rust` representation]: <https://doc.rust-lang.org/reference/type-layout.html#the-rust-representation>
/// ///
/// In addition, all *safe* function pointers implement [`Fn`], [`FnMut`], and [`FnOnce`], because /// In addition, all *safe* function pointers implement [`Fn`], [`FnMut`], and [`FnOnce`], because
/// these traits are specially known to the compiler. /// these traits are specially known to the compiler.